Modern cellular telephone systems currently utilize high power, frequency, time and/or code division multiplexed narrowband radio frequency communication techniques to in conjunction with large cells to establish and maintain telephone communications. With the growing popularity of mobile stations configured for operating in these systems, increased flexibility and convenience in user utilization of these mobile stations is desired. One approach to providing user flexibility and convenience while encouraging greater utilization of the mobile stations is by combining the functionality of a cellular mobile station with that of a cordless mobile station, thereby allowing a single cordless/cellular station to make and receive telephone calls either via the cellular network when the cordless/cellular station (or cordless/cellular telephone (CCT)) is out of range of a home cordless base station, or via landlines of the public-switched telephone network (PSTN) when the cordless/cellular station is within range of a home cordless base station. Cordless operation typically uses a frequency band different from that during cellular operation, and typically, separate telephone numbers are used for cordless and cellular operation: each home cordless base station has a land-line subscriber telephone number through which all incoming and outgoing calls are routed, and a mobile identification number (MIN) is assigned by the cellular network provider to the cordless/cellular station.
In U.S. Pat. Nos. 5,127,042 and 5,463,674, to Gillig et al., which are herein incorporated by reference, when a cellular cordless telephone is within range of a cordless base station, telephone calls can be made over the cordless radio channel or transferred from the cellular radio channels to the cordless radio channel. Telephone calls may be made over the cellular radio channels or transferred from the cordless radio channel to one of the cellular telephone channels.
Although systems employing cordless/cellular stations have been proposed such that both cordless and cellular operation may be provided coherently and seamlessly, two separate telephone numbers--a mobile identification number (MIN) for cellular operation and a land-line telephone number for cordless operation--are required, thus giving rise to a reachability problem. That is, a caller who dials the land-line telephone number will not reach the user of the cordless/cellular station when it is not within range of the home cordless base station. Such a caller would then be required to dial the MIN, assuming both telephone numbers are known to the caller. Alternatively, the home cordless base station may be adapted to employ call forwarding such that calls received by the home cordless base station when the cordless/cellular station is not within range are forwarded by the home cordless base station over a second line to the cordless/cellular station MIN. Such a call forwarding mechanism employing a second call over a second line, however, is costly and inefficient with respect to time, resource allocation, and concomitantly money.
Accordingly, there is a need for improved operability of cordless/cellular telephones, and particularly for a method and apparatus that allows a call placed to a land-line telephone number associated with a cordless/cellular telephone to be efficiently forwarded, without using a second line, to a MIN associated with the cordless/cellular telephone when it is not within range of the home cordless base station.